DE102009026606A1 - Digital hydraulic controller - Google Patents

Abstract

The invention relates to a digital hydraulic controller with at least two valve element rows, of which one valve element row can connect a supply line to a controller output and the other valve element row can connect the controller output to an outlet line. In the regulator, the valve elements of each valve element row are connected in parallel and can be switched simultaneously or individually in different combinations with each other. The valve elements of a valve element row each have a different flow cross-section. According to the invention, the valve element, which has the smallest flow cross-section, is present twice in the valve element row. It is also described a system unit with a differential cylinder and a digital hydraulic controller having four valve element rows, two of which are connected with their common regulator output to the one pressure chamber of the differential cylinder, while the other two valve element rows with their common regulator output to the other pressure chamber of the differential cylinder are connected. Due to the independent adjustment of the pressures in the two pressure chambers, the differential cylinder can be used as a precisely adjustable linear actuator.

Description

The The invention relates to a controller, particularly in a hydraulic system for a machine for producing a fibrous web, z. As a paper or board machine, is used.

In Paper machines is widely used hydraulics as actuation and control means used; in particular, actuators hydraulically driven, with which large forces adjusted and exercised with high accuracy.

In usually a working fluid, z. B. Hydraulic oil used, which is pressurized by a pump. The introduction of the pressurized hydraulic oil into a hydraulic Actuator, such as. B. a hydraulic cylinder or a hydraulic motor is typically by a proportional control valve or proportional valve controlled, driven electrically, hydraulically or pneumatically can be.

One such control valve has a displaceable or displaceable spool or control piston, which in response to its location in an associated Valve housing can set a target pressure at the output, by the pressure of hydraulic oil supplied by the pump is regulated down. The mobility of the spool in the valve body necessarily requires a certain clearance or gap between Control spool and valve body, allowing internal leakage of the control valve is unavoidable. The gap size must not Too narrow, otherwise the valve would too susceptible to contamination in the hydraulic oil.

In Lately, alternative pressure regulators have been developed in this Registration throughout as digital hydraulic pressure regulator should be designated. Become such digital hydraulic pressure regulator used as a pressure reducer, these are in the present application throughout referred to as digital hydraulic pressure reducer.

The operation of the digital hydraulic pressure regulator or pressure reducer is for example in the journal Fluid No. 7-8, 2008, pages 12, 13 described. The improved readability of this application, the method of operation of digital hydraulic pressure regulator is briefly summarized:
In the simple case, a digital hydraulic pressure regulator consists of a series of valves connected in parallel, which have only ON / OFF functions; So are simple ON / OFF switching valves that allow or interrupt a flow and can be consistently referred to in this application as valves. The valves are all connected to a common supply line on the one hand and to a common output line on the other. The valves themselves may be conventional solenoid valves, ie valves with electromagnetic drive. Of course, other forms of drive can be chosen.

By Connection or installation of throttle elements or through the valves itself is ensured that the valves are different Have flows when they are open. If For example, four valves are provided, so can the flow rates Q in the individual, each of the associated Valve optionally releasable passages in proportion of 1: 2: 4: 8 to each other; at a larger one Number of valves will continue this series accordingly.

By opening and closing individual valves or valve combinations, based on mathematical models of a calculator determined and selected, can now be a very fast and precise pressure adjustment in the output line or be achieved in the connected actuator. this will achieved by the analog control curve of the above-described proportional Control valve through a digitally created (approximated) Rule curve is replaced. This curve may be due to the omission of Non-linearities and / or hysteresis of the analog proportional valve be a stepped approximate straight line that allows a control point fast and (almost) free of overshoot to approach.

In the pressure regulators of the type mentioned are several valves (hereinafter referred to as valve elements, which has a switching valve function and have a rigid throttle function) independently actuated. The control curve is displayed by switching suitable combinations of the valve elements at the same time. If a single valve element stops working, decreases the accuracy of the Control off, but the control function remains.

task The invention is to propose a digital hydraulic controller the simple means a high control precision also ensures failure of a valve element.

These Task is with a digital hydraulic controller with the features of claim 1.

It It has been found that valve elements with low flow rates, So the small flow cross sections, for the Precision of the control of crucial importance are and that these valve elements are also those valve elements, which are most frequently used.

This was used as a special example in the regulation of line load in a hydraulic cylinder actuated nip of a Kalanders examined and the statement that the valve elements with the low flow, so the small flow cross sections, for the precision of this regulation of decisive Meaning, has been confirmed.

Has according to the invention a digital hydraulic controller at least two valve element rows, from where the one valve element row a supply line with a Controller output can connect and the other valve element series the Controller output can connect to an outlet line. The valve elements each valve element row are connected in parallel and individually or simultaneously switchable in different combinations with each other. Have at least some of the valve elements of a valve element row a respective different flow cross-section. According to the invention at least the valve element of each valve element row, the smallest Flow cross-section has double in the valve element series available.

On This way it is ensured that in case of failure of the valve element with the smallest flow area through redundancy of this Function maintained a consistent control quality remains.

The taken arrangement also has the advantage that experience shows also nominally identical valve elements actually slightly have different flow cross-sections or different Let through throughputs. These differences can be used in a digital hydraulic controller to that in the determination of a switching combination of valve elements for a regulator intervention, the more suitable of the two valve elements smallest flow is selected. Leave it to refine the regulation even further.

Preferably are the valve elements from an electromagnetic switching valve and a throttle provided on the valve. The Chokes can be made by simple holes and can then be combined with always the same valves become. In this way are the elements that have moving parts and thus are susceptible to failure, always the same. This Makes both the construction cheaper and simplifies the stocking of spare parts.

Preferably are within a valve element series, the valve elements with different flow cross-sections assembled so that they one from valve element to valve element have gradually increasing flow cross-section. Preferably the flow cross-section is doubled from stage to stage.

In an advantageous embodiment form the flow cross-sections a binary row, in the smallest flow area 1 and the other flow cross sections 2, 4, 8 and 16, etc. amount.

Preferably is the digital hydraulic controller according to the invention designed so that switching valves and throttles for use with liquids, especially for hydraulic oil, designed and suitable; Alternatively, switching valves and chokes can be used with gases, especially for compressed air, designed and suitable be. The switching valves can be electromagnetically be driven valves.

In Application of the invention, the controller with a controller be connected, the switching valves or the switching valve combinations to open controls, the controller as the controller pressure regulator or as a flow regulator can control.

The Invention is to a system unit with a differential cylinder and a digital hydraulic controller applicable in which the controller has four valve element rows, two of which with their common Controller output with a cylinder-side pressure chamber of the differential cylinder are connected while the other two valve element rows with its common regulator output with a piston rod side Pressure chamber of the differential cylinder are connected. In this System unit can be in one from the controller output to the cylinder side Pressure chamber leading line arranged a flow sensor be. In this embodiment, the flow sensor as a position sensor used as will be described later.

Special Advantages then shows an arrangement with two such system units, in each differential cylinder at a bearing point one at their both ends bearing roller attacks, the control unit the signals of the flow sensors as position information of the evaluates each roller end and the movement of the two differential cylinder synchronized based on this position information.

Various Applications of the regulator according to the invention are explained below.

As a rule, the force generated by a differential cylinder, ie a double-acting hydraulic cylinder with two chambers each bounded by a piston side, is generated the pressure in one chamber of the cylinder is set only while ambient pressure or the pressure in the storage tank (tank pressure) prevails in the other chamber.

If the cylinder should "press" (eg the piston rod is to be extended), the pressure in the piston-side chamber elevated. Otherwise, if the cylinder should "pull" (eg the piston rod is to be retracted), the pressure in the rod-side chamber increases.

in the Case of a load change from push to pull or vice versa, the control passes through a condition (dead area) in which no force is exerted by the cylinder, in In this state, both chambers have tank pressure. In this condition Both chambers are connected to the tank and the piston is in a sense loose or free.

If also to cover a large range of forces it is difficult, according to sensitive regulations to provide an accurate control of small forces to ensure.

With the precision of a digital hydraulic pressure control it is possible both chambers of the differential cylinder simultaneously pressurizing and the pressure in the chambers independently of each other. In this way it is possible even very small forces that exert the hydraulic cylinder should set, by both pressure chambers at a high pressure level have correspondingly set pressure differences, so the force setting by counter-pressure in working against the desired force Pressure chamber takes place or is supported.

in addition Yet another advantage is the precision of the digital hydraulic Regulation is better when the inlet pressure in the regulator and the Output pressure from the regulator are similar, d. H. when the pressure drop across the regulator is small is. This means that the pressure in both chambers is close the supply pressure (input pressure of the regulator) are kept so that that is a valve element within its minimum opening time flowing through volume is small, and thus just the sensitive control in the range of small changes is improved. To reinforce this positive effect, The control unit can be designed so that the pressures so chooses that the higher of the two chamber pressures only slightly below the supply pressure. Thereby becomes independent of the forces to be generated always regulated in the area of best control precision.

By the simultaneous pressure control in both pressure chambers is further the change between pushing and pulling in the differential cylinder considerably better controllable; it is enough if only by change the pressure in a pressure chamber appropriately increases the counterforce or is decreased so as to exceed the force of the other pressure chamber or to fall below. This does not result in an uncontrolled state more in which both pressure chambers are connected to the tank.

A typical application of digital hydraulic control technology is the control of pressing pressures of rollers and control of pressure gradients in a nip in the cross machine direction CD (CD = cross machine direction).

These Digital hydraulic technology can also be used around the bezel a headbox nozzle (slot nozzle) in one Paper or board machine. Üblicherweis Adjusting the aperture, the CD direction is a uniform Leakage from the nozzle slot of a headbox to ensure, by means of electric spindle drives. These equipped with stepper motors and a suitable gearbox Actuators are close to each other (about every 75 to 150 mm) along the Aperture attached and the adjustment of the slot width of the slot nozzle is done by local (slight) bending of the lower edge the aperture in the direction of the lower edge of the slot nozzle.

By the precision of the regulation with the digital hydraulic Technology of the kind described is achieved and because of this Hydraulics includes a once set pressure in a volume and then maintain it without further effort, it is possible, the aperture adjustment by means of differential cylinders to accomplish instead of the usual spindle drives to use. In this way, one can be in the construction realize simple and low-maintenance aperture adjustment.

In This solution is in each case instead of a spindle drive in a usual headbox, a differential cylinder provided, the piston rod with a displacement or position sensor is connected to a precise set value for the piston position to obtain. As position sensors can be different Sensor types are used; for the on a headbox the prevailing environmental conditions is a so-called LVDT sensor (LVDT = Linear Variable Differential Transformer) because of its robustness particularly suitable. Other sensor types can be used become. For a regulation may also be a force as Feedback size can be used.

Depending on the requirements of the positioning speed and positioning accuracy, a simple digital hydraulic controller with twice two to three valve elements (switching valves with throttle) are provided which adjusts the pressures in the two pressure chambers with feedback of the actual position so that the aperture sets the desired slot width. It is possible to equip each differential cylinder with its own valve elements.

If the required operating times allow this, but can also solutions are chosen in which, for example in a kind of multiplexing only one controller is present, the the pressures for two pressure chambers in two central Can set pressure lines. The individual differential cylinders be in this multiplexing successively individually with the connected to central pressure lines and the set pressures in the two chambers of this differential cylinder are then from adjusted to the central pressure regulator. In this case, the individual position sensor provide a size for the setting. Then the two chambers are closed and thus also by the separate central lines. In this way two are enough simple switching valves for each differential cylinder and it can be done with very few wires.

It Mixed forms are also possible in which groups of differential cylinders in multiplexing individually or together in superposition of a mechanical (pre) adjustment can be adjusted. Of course, each differential cylinder can have its own Be assigned controller.

For the pressure supply is sufficient because of the low frequency the setting and because of the short travel a very small Pump, which expediently with a pressure accumulator is coupled so that an approximately constant input pressure at the Regulator or the regulators is sufficient.

In 1 an arrangement of such a differential cylinder for diaphragm adjustment is shown schematically with only one cylinder.

The differential cylinder 1 has two pressure chambers 11 and 12 , The piston rod of the cylinder 1 is fixed with a shutter 6 coupled and the cylinder 1 is effective to the aperture 6 in 1 up and down to adjust.

cables 21 and 22 are with the associated pressure chambers 11 and 12 connected to a pressure regulator 2 connected, which is a digital hydraulic controller, which has been previously described in detail. A control unit 3 receives as information a position signal x, which is output from a position sensor (not shown), and the two pressures in the chambers 11 and 12 , Further factors influencing the desired chamber pressures or the setpoint position of the piston rod (or the diaphragm) can result from calculations, other specifications or measured variables, etc. These specifications of the controller 3 Following is the pressure regulator 2 then the desired pressures in the chambers 11 and 12 one.

Furthermore, in 1 another supply unit 4 provided with pump and tank for the working fluid and reference numerals 5 shows a pressure accumulator.

When Working fluid comes along with common hydraulic fluids also water and / or aqueous emulsions into consideration what easy to handle, and does not pose an environmental risk. Because only small movements are carried out and in the pressure regulator only On / off switching valves are used, the lubricity of hydraulic oil is not essential.

2 shows an arrangement for detecting the piston position of differential cylinders 1 in a hydraulic system with digital pressure regulators 2 ,

A pump 10 delivers via a flowmeter 51 that of the pump 10 measured volume flow of working fluid supplied to the system, working fluid to two pressure regulators 2 , each with a differential cylinder 1 are connected. The delivery pressure of the pump 10 and possibly the temperature at the measuring point 14 detected. Flowmeter 52 detect the flow of working fluid into the cylinder-side pressure chamber of the respective cylinder 1 , The measuring points 19 provide measured values of the pressures and possibly temperatures in the pressure lines to the cylinders 1 , Due to the lossless operation of the digital hydraulic pressure regulator 2 corresponds to that of the flow meters 52 detected amount of working fluid actually present in the respective cylinder-side pressure chambers filling amount, which is a reliable measure of the piston position.

Moving heavy loads such. B. rolls in a paper machine, with two hydraulic cylinders 1 is always a synchronization problem of the movement of the two piston rods. The result of the flow measurements is a position sensor for the piston position, with the flow meter 52 should measure accurately. Preferably, gear systems are used that are relatively accurate. In addition, the flow measurement with the flowmeter provides 51 in the supply line another measured value, the plausibility check of the results of the flow meter 52 can be used for the pressure chambers.

Due to the indirect measurement, the absolute value for the piston position can also be slightly faulty, but it can be the two measured values (depending the one for a cylinder 1 ), which are detected at the same time and are exposed to the same external influences, indications are taken as to how synchronously the two pistons move, or whether the movements deviate from one another to an excessive extent. These findings can be used to improve synchronization, if necessary, with appropriate measures. Furthermore, it can also be concluded from the measured values of malfunctions in the hydraulic system.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Fluid No. 7-8, 2008 pages 12, 13 [0006]

Claims (14)

Digital hydraulic controller having at least two rows of valve elements, one valve element row connecting one supply line to one controller output and the other row of valve elements connecting the controller output to an outlet line, the valve elements of each valve element row connected in parallel and switchable individually or in various combinations with each other, and at least some of the valve elements of a valve element row have a respective different flow cross-section, characterized in that at least the valve element of each valve element row, which has the smallest flow cross-section, is double in the valve element row. A digital hydraulic controller according to claim 1, wherein the valve elements of an electromagnetic switching valve and a valve provided on the throttle are composed. Digital hydraulic controller according to claim 1 or 2, characterized in that within a valve element row the some valve elements one from valve element to valve element have gradually increasing flow cross-section. Digital hydraulic controller according to claim 3, characterized characterized in that the flow cross section of step doubled to level. Digital hydraulic controller according to claim 1 to 4, characterized in that the smallest flow cross-section 1 and the other flow cross sections 2, 4, 8 and 16 amount. Digital hydraulic controller after one or more of claims 2 to 5, wherein switching valves and throttles for use with liquids, especially for Hydraulic oil, designed and suitable. Digital hydraulic controller after one or more of claims 2 to 5, wherein switching valves and throttles designed for use with gases, especially for compressed air and are suitable. Digital hydraulic controller according to claim 6 or 7, characterized in that the switching valves electromagnetically are driven valves. Digital hydraulic controller after one or more of the preceding claims, characterized in that the controller is connected to a controller that controls the Switching valves or the switching valve combinations for opening controls. Digital hydraulic controller according to claim 9, characterized in that the control unit controls the regulator as a pressure regulator controls. Digital hydraulic controller according to claim 9, characterized characterized in that the controller is the controller as a flow controller controls. System unit with a differential cylinder and a digital hydraulic controller according to one of the preceding Claims 1 to 11, wherein the controller four rows of valve elements of which two with their common controller output with a cylinder-side pressure chamber of the differential cylinder connected are, while the other two valve element rows with their common regulator output with a piston rod side Pressure chamber of the differential cylinder are connected. System unit according to Claim 12, characterized that at least in one of the controller output to the cylinder side Pressure chamber leading line arranged a flow sensor is. Arrangement with two system units according to claim 13, characterized in that each differential cylinder on a Bearing point attacks a roller mounted at both ends, wherein the control unit signals the flow sensors as Evaluates position information of the respective roll end and the Movement of the two differential cylinders based on this Position information synchronized.